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Healthy Fruit 1997 Vol. 5:16

Jul 23, 1997

Apple Maggot Migration Increases

Although apple maggot flies have not invaded in particularly large numbers over the past week, there are some monitored blocks where trapped AMF have reached significant levels, averaging 4 to 5 per trap. While fruit in most areas remain free of AMF stings, some areas of high AMF capture have sustained up to 2% injury on McIntosh, with earlier-ripening varieties even more susceptible to AMF damage at this stage of the season. Growers should be on the lookout for increasing AMF damage from this point on. Some growers have chosen to use Lorsban for early-season AMF control; this material does offer some control of low AMF populations with simultaneous control of woolly apple aphids and leafhoppers. However, at this point in the growing season, when AMF populations begin to grow rapidly, we recommend switching to Guthion or Imidan for the most effective AMF control.

Red Mite Miticide Might Miss

In one orchard, a treatment of Kelthane against ERM was totally ineffective. This ineffectiveness is not entirely surprising; similar results have been seen in several orchards over the past couple of years. Even if a grower has not used Kelthane for many years, chemicals of this nature (chlorinated hydrocarbons) are notoriously subject to development of resistance by mites. Development of such resistance was enhanced by widespread use of these chemicals in the past, and can be carried in the genome and passed from generation to generation over the course of decades. A grower should not expect optimal performance from a Kelthane treatment unless no related chemicals have been used in the past 40 years. If a mite problem develops which warrants treatment, we recommend an application of either Pyramite or Vendex.

Meanwhile, some orchard blocks treated with Savey, Apollo or Agrimek have shown recent increases in European red mite populations, but the majority of those blocks treated with an early-season miticide appear to be holding up well. Where Pyramite has been used as a summer mite treatment, results have been good after a single application. In fact, very low survival has been observed of ERM nymphs hatching up to 10 days after an application of Pyramite.

Gen Two Leafminer Fizzle

In most orchards, the time for treatment against second-generation leafminer adults has passed. However, in samples made across many orchards, very few tissue-feeding mines of the second generation have been observed. This low number of second-generation LM is likely due to widespread, effective first-generation LM treatments.

Potato Leafhoppers Devastate Young Block

In one orchard observed last week, damage caused by potato leafhopper was easily the worst seen in recent history. In new plantings of trees, virtually every leaf was curled and burned by PLH. In this case, the grower was away for 10 days and the PLH population built up to extreme levels in his absence, with a devastating effect on young, unbearing trees.

As mentioned in previous issues of Healthy Fruit, there is no evidence to date that PLH cause significant damage on established, fruit-bearing trees. Growers with young trees should continue to monitor for buildup of PLH adults and nymphs. PLH nymphs are bright green, and generally move around very nervously on leaves, preferring to stay out of sight on the bottom side. Adult PLH also have a green cast, as opposed to white apple or rose leafhoppers, which are both white. Experience in Massachusetts shows that Guthion, Imidan, Lorsban, Sevin and Thiodan are all effective treatments against leafhoppers, even at half-rates. In New York state, the feeling is that Guthion and Imidan are weak, even ineffective, in controlling LH populations. To date, this has not been observed in Massachusetts. Populations of white apple and rose leafhopper are low in most areas of the state, as early season treatments of Provado and Agrimek offered strong suppression of both.

Woolly Aphid Build-Up

As reported last week, woolly apple aphid populations continue to grow, spreading into new terminal growth. Trees should be checked regularly for WAA infestation, especially in pick-your-own blocks, where tolerance is lower. Population levels of WAA need to be kept in check, as the amount of honeydew which they secrete can lead to the development of sooty mold fungus. A treatment of either Lorsban or Thiodan should provide good control.

Dogwood Borer Wars

According to researchers in New York state, many young trees are showing infestation of dogwood borer, particularly in the burr knot tissue. If evidence of borer infestation is shown, now is a good time for a trunk treatment; where necessary, use a dilute spray of Lorsban 50WP or Thiodan 50WP.

Peaches Getting Bored Too

Relatively heavy infestations of borers have been observed in blocks of young peach trees this year. At this point, it is fairly late to begin trunk applications, though such a treatment can be effective as a deterrent to further egglaying. For such a treatment, we recommend use of Lorsban.

Pear Psylla

Pear psylla populations have progressed into the adult stage; a stage of development which is not particularly susceptible to insecticidal control. Against nymphal stages, applications of Mitac have appeared to work well thus far.

Fungi Don't Like Dry Summer

The dry summer should reduce fungicide needs in apple and peach orchards. For example, spray intervals for simple captan applications against flyspeck can be increased to at least 3 weeks. If the weather patterns hold as they have so far, then growers should need only one more fungicide application against flyspeck in those areas where flyspeck is generally a problem. In blocks which don't generally have sooty blotch or flyspeck, consider stopping summer fungicides now.

In peaches, go with the minimum number of fungicide applications. In general, one application of a good brown rot fungicide within 3 days of harvest should be enough to keep brown rot at bay this season.

Of course, it could always start raining again, changing the situation dramatically.